Field sampling of liquids contained in wells, barrels, surface or subsurface reservoirs, storage tanks and the like is commonly accomplished by immersing an empty vessel in the liquid, withdrawing it when full, and transferring the contents from the vessel to a transport container by pouring the contents from one to the other. At a later time the transport vessel is opened at a laboratory and the sample is analysed. The procedure serves satisfactorily for determining components present in gross amounts, but is unsatisfactory for measuring minute quantities of components, or for obtaining an accurate analysis of components which can be altered or lost due to aeration or volatilization. It is particularly important to utilize appropriate procedure and means for obtaining accurate analysis when testing for trace amounts of environmental pollutants, e.g. hydrocarbons, pesticides or heavy metals in water samples, and for avoiding sample contamination.